The present invention relates to a liquid crystal display device of a liquid crystal television set, a liquid crystal display for a cellular phone, and the like, which performs a display by modulating a linear polarization state, and more specifically, to a liquid crystal display device capable of outputting an audio from a screen itself.
In recent years, liquid crystal display device technology, and particularly, liquid crystal display device technology using color display elements has significantly progressed. In the liquid crystal display device, downsizing/thinning, weight reduction, and further, lower power consumption, can be achieved. Accordingly, demand for liquid crystal display devices has rapidly expanded. Such a liquid crystal display device has a configuration in which an element (liquid crystal cell) formed by sandwiching a liquid crystal layer between a pair of glass substrates is provided, and polarizing plates are attached onto a light incident side and light emitting side of the liquid crystal cell. Then, in the liquid crystal display device, typically a transmissive liquid crystal display device, a liquid crystal cell is illuminated from behind by a backlight, and a polarization state of a linear polarization incident onto the liquid crystal cell is modulated by a liquid crystal layer, and thus a display is performed.
The liquid crystal display device has also been utilized actively for a portable information terminal such as a cellular phone and a personal digital assistant (PDA), a car navigation device, and the like, by making use of such characteristics thereof that it is possible to achieve the downsizing/thinning, the weight reduction, and the lower power consumption. In such a portable information device, it is also necessary to output audio information in addition to image information, and accordingly, the information device mounts a speaker thereon. In order to achieve further downsizing/thinning and weight reduction of such an information device, technologies which enable an audio output without using a conventional speaker have been proposed.
For example, there is a technology regarding an electrostatic transparent speaker composed of a transparent vibration plate on which a transparent electrode film is formed; a transparent fixing plate on which a transparent electrode film is formed, the transparent fixing plate being opposite to the transparent vibration plate; and an insulating spacer frame which is provided between the transparent vibration plate and the transparent fixing plate and forms a closed space together with the transparent vibration plate and the transparent fixing plate. The electrostatic transparent speaker is used by being attached onto a front of a display or the like such that the other side of the speaker can be seen from outside through transmission regions of the transparent vibration plate and the transparent fixing plate. For example, refer to Japanese Patent Laid-Open No. Hei 10 (1998)-191496 (pp. 3-5, FIG. 1).
Moreover, there is a technology for generating a sound by the following configuration. Between glass substrates constituting a liquid crystal cell, on a glass substrate located on a backside of a screen, a silicon thin film where electrons which transmit image and audio signals can move at high speed is coated, and on the same silicon thin film, a circuit for displaying an image and an audio circuit are arranged. Then, an electric signal is transmitted to a sound source element (exciting source element) attached onto the glass substrate, and the glass substrate located on a front side of the screen is vibrated, and thus the sound is generated. For example, refer to the Internet <URL:HYPERLINK“http://www.asahi.com/tech/asahinews/OSK2003091” http://www.asahi.com/tech/asahinews/OSK2003091 90044.html>.
In such modes of outputting the audio from the screen itself, for example, in a case of using such modes for a cellular phone, a sound source portion of the cellular phone becomes larger as compared with that of a conventional cellular phone. Accordingly, it becomes possible to reproduce a high-quality audio, and audio quality of a ring tone and a conversation can be enhanced. Moreover, in the case of browsing a moving picture, for which use of a third generation cellular phone is expected to be expanded, it also becomes possible to reproduce a realistic sound while displaying an image. Also with regard to a structure of the cellular phone itself, a speaker for listening to a voice of a party on the other end becomes unnecessary, and a speaker for reproducing the ring tone also becomes unnecessary, thus making it possible to further progress the downsizing/thinning and the weight reduction of the device.
However, in externally attaching the electrostatic transparent speaker onto the liquid crystal screen as in the technology described in the above-mentioned Patent reference, an image is seen through the transparent speaker because the transparent speaker is attached onto the front of the screen. Accordingly, there is a disadvantage in that harmful effects such as a decrease in the light quantity of the image and a difficulty in seeing the image due to reflection.
In an alternative technology, between the glass substrates constituting the liquid crystal cell, the glass substrate itself located on the front side of the screen is vibrated to generate the sound. Accordingly, the technology has an advantage for a user in that the disadvantages of the difficulty in seeing the image and the like are extremely small.
Although it is desirable to form the glass substrates constituting the liquid crystal cell as thin as possible in order to achieve the downsizing/thinning and weight reduction of the liquid crystal display device, defective regions of glass of the glass substrates are decorated and substrate surfaces are prone to be uneven when the glass substrates are thinly formed. The unevenness of the surfaces of the glass substrates brings an image display failure in the liquid crystal display device, and accordingly, a thickness of each of the glass substrates sandwiching the liquid crystal layer therebetween, which is obtained by processing the glass substrates to be thin, has had a lower limit of approximately 0.6 to 0.7 mm. Therefore, weights of the glass substrates themselves cannot be reduced sufficiently, and it is difficult to vibrate the entire glass substrate sufficiently, and thus there is a problem that a sufficient volume cannot be ensured.